Moulding compositions

ABSTRACT

Fire resistant compositions comprising a thermoplastic polymer, chrysotile asbestos, and an additive mixture of an antimony compound and a halogenated hydrocarbon.

Umted Sta O/ Wicker v Dec. 23, 1975 MOULDING COMPOSITIONS 3,331,797 7/1967 Kopetz et al 260/28.5 3,576,784 4/1971 Gloor 260 4245 [76] George 1 LoYhouse 3,640,929 2/1972 Darling 260/23 H Close, Mllnrow, Lancashlre, 3,654,202 4/1972 Eusebi 260/23 H England [22] Filed: 1974 Primary ExaminerJames H. Derrington [21] Appl. No.: 494,252 Attorney, Agent, or Firm-Lawrence Rosen; E. Janet Related US. Application Data Berry [63] Continuation-impart of Ser. No. 260,153, June 6,

1972, abandoned.

[57] ABSTRACT 52 U.S. Cl. 260/37 N; 106 15 FP; 260/42.44;

260/4245; 260/45 7 2 0 45 75 3 Fire resistant compositions comprising a thermoplastic [51] Int, Cl, C08K 3/22; (103K 5/03; (303 7 12 polymer, chrysotile asbestos, and an additive mixture [58] Field 6: Search 260/4244, 42.45, 37 N of an antimony compound and a halogenated y carbon. 1

[56] References Cited UNITED STATES PATENTS 3 Claims Drawmgs 3,090,764 5/1963 Ellis et al. 260/42.45

MOULDING COMPOSITIONS This application is a continuation-in-part of SerrNo. 260,153 filed June 6th, 1972, nowabandoned.v

Thermoplastic polymeric materials are increasingly used in place'of metals for the manufacture of various articles and parts but they suffer from lack of resistance to ignition. In particular, polyoleflns, especially polypropylene and copolymers of propylene, are notoriously poor in resisting ignition and spread of fire. This is the more unfortunate as polypropylene and copolymers of propylene, because of their resistance to deformation at elevated temperatures, are used for automobile heater ducts and other under-bonnet and interior parts and for such uses resistance to ignition and spread of fire are obviously important requirements. This requirement for resistance to ignition is also met in other fields in which thermoplastic polymeric materials are used and with other materials such as polystyrene and polyamides.

It is well known that the improved resistance to ignition and burning of thermoplastic polymeric materials can be produced by the incorporation of various additives, of which the most commonly used are halogenated hydrocarbons and antimony trioxide, but which include phosphorus and boron compounds. Combinations of antimony trioxide and halogenated hydrocarbons can act synergistically in suppressing the burning of polymeric materials and so are particularly useful.

The proportions of any such'additives required to suppress the burning of polyoleflns and other polymers are however, so high as to resultin a considerable, and in some cases unacceptable, reduction in the resistance of deflection at elevated temperatures and in a worsening of mechanical properties such as tensile strength, flexural strength and impact strength. The additives are expensive and the high proportions required often make the price of the final products uncompetitive. In addition, the additives reduce the resistance to weathering and can be leached out by weathering or solvents, thus resulting in a lowering of the resistance to ignition.

To reinforce polymeric materials by glass fibres is well known and if glass fibres are incorporated in polymeric materials rendered fire resistance by additives such as those described above, the mechanical properties and resistance to deflection at elevated temperatures are usefully improved but the cost of the materials is increased even further.

It is also known to reinforce polymeric materials with asbestos fibres, and it has been claimed that improved physical properties can be obtained by chemically treating the surface of chrysotile asbestos fibres whereby the treated fibres may be incorporated into synthetic resins and chemicallycombined therewith.

I have made the suprising discovery that if chrysotile asbestos is incorporated, in selective proportions with fire retardent additives, into thermoplastic polymeric materials, commercially acceptable fire retardant ratings and mechanical properties are achieved, using much less of the fire retardant additives than is necessary to obtain acceptable suppression of burning of the polyolefins and other polymers as referred to above.

I believe that this effect is due to the chrysotile asbestos fibre exhibiting, at least in the compositions of this invention, a fire retardant additive property not hitherto recognised; this property is additional to (and not equivalent to, nor a result of) the very well known property of flame resistance.

According to the present invention, I provide fire resistant thermoplastic compositions comprisng a. at least 40 percent, and generally about 40 to percent,.thermoplastic polymer such as polypropylene, copolymers of propylene, polyethylene, polystyrene, styrene/acrylonitrile copolymers, polyamides, and mixture thereof;

b. from 5 to 40 percent, and preferably from 20 to 40 percent, by weight of chrysotile asbestos fibres; and

c. from 2.5 to 20 percent by weight ofa fire retardant additive selected from the group consisting of halogenated hydrocarbons and mixtures of a halogenated hydrocarbon with a fire retardant inorganic compound.

The inclusion of the chrysotile asbestos fibres provides the suprising result that the proportion of fire retardant additive required to give a particular level of fire resistance can be reduced considerably below the proportion which would be expected to be necessary on the basis of the effects of including chrysotile asbestos fibre and a fire retardant additive separately into thermoplastic polymers. This discovery is surprising since the fire resistance of thermoplastic polymers is generally not greatly affected by the inclusion of chrysotile asbestos fibres in the absence of a fire retardant additive and, in the case of certain thermoplasticpolymers giving rise to relatively low viscosity meltseg. polyamides such as nylon 6, the inclusions of chrysotile asbestos fibres alone in proportions up to about 10 percent by weight appreciably worsens the fire resistance of the polymers.

The fact that chrysotile'asbestos apparentlyacts as a fire retardant additive is most advantageous since the asbestos fibres are exceedingly cheap in comparison to fire retardant additives which are, as already mentioned, expensive. Thus, even if the amount of the chrysotile asbestos fibres used in order to achieve a given fire resistance is considerably greater than the reduction in the amount of fire retardant additive-necessary, the final products are still cheaper.

The chrysotile asbestos fibres are also of great value in that, unlike fire retardant additives, they improve the mechanical-properties of the materials. Thus, the inclusion of thechrysotile asbestos fibres at least offsets any disadvantageous effect on the mechanical properties caused by the fire retardant additives and, depending on the proportion of the fibres, the mechanical properties of the compositions may be considerably better than those of the thermoplastic polymers themselves. As already mentioned, glass fibres can be used to reinforce polymeric materials thereby improving their mechanical properties and resistance to deflection at elevated temperatures but glass fibres only have a slight cooperative effect on fire resistance when used with fire retardant additives compared with the considerable beneficial cooperative effect produced by use of chrysotile asbestos fibres with a fire retardant additive in a thermoplastic polymer. This distinction is quite unexpected since glass fibres, like chrysotile asbestos fibres, when used alone in thermoplastic polymers generally have little effect on fire resistance and, again like the asbestos fibres, tend to worsen fire resistance in the case of some thermoplastic polymers e.g. ones giving rise to relatively low viscosity melts.

What makes the apparent fire-retardant property of chrysotile asbestos even more surprising is that other forms of asbestos such as anthophyllite and amosite do 3 not exhibit the same beneficial effect if substituted for chrysolite asbestos in the compositions of this invention.

By enabling a given fire resistance to be obtained by face of the bar. The first line is at 25 mm in from one end and the second line is at 127 mm from the same end. The igniting flame is applied to that end. The bar is clamped so that its length is horizontal and its width use of smaller proportions of fire retardant additive the 5 is tilted at 45 to the horizontal and the flame is applied use of chrysotile asbestos fibres is beneficial in that the for seconds. flow propertiesof the compositions under moulding In the above test method, if, after application of the conditions are less affected by the additives and the flame, the material does not burn to the first mark and adverse effect on fire resistance of weathering and does not flame for more than 5 seconds after removal solvent leaching of the additive is reduced. 10 of the flame, the material is classed as self extinguish- An additional advantage of the compostions of this ing. If the material burns beyond the first mark, but invention is that, for a given fire resistance rating, the the flame does not reach the second mark, the material density of the smoke generated in the case of fire is is classed as Resistant to flame propagation. If the reduced, and hence a reduction in toxicity is achieved. materials burn beyond the second mark, the rate of The compostions according to the invention as iniburning in mm per minute is recorded. tially manufactured will usually be in the form of par- Compositions according to the invention are selfticulate moulding compositions. Such composition can extinguishing or resistant to flame propagation under be made by known methods such as extrusion comthe conditions of the above test. pounding a melt of the polymer with the asbestos fibres The following examples illustrate the invention. In and the additive and granulating or pelleting the ex-' the examples the test method described above was trudate. The moulding compositions may be used in the used. In the tests it was also observed whether or not manufacture of moulded or extruded articles. burning fragments dripped from the test material and The proportions of the components in the composiwhat happened to the fragments and remaining test tions according to the invention can vary widely within portion if such fragments did drip. As far as the spread the above ranges depending on the particular mechaniof fire is concerned the dripping of burning fragments is cal and fire retardant properties desired and on the a particular hazard. The examples show that not only nature of the components. For a composition comprisare the chrysotile asbestos fibres greatly superior to ing given components the amount of fire retardant glass fibres and to anthophyllite or amosite asbestos as additive required to achieve a given fire resistance will far as burning of the test specimens themselves is connaturally depend, within limits, on the amount of the cerned but that the chrysotile asbestos fibres are also of chrysotile asbestos fibres. As it will often be desirable, greater utility in preventing the dripping of burning for the sake of mechanical properties, to include quite fragments. substantial proportions of asbestos fibres, eg. 20 percent by weight or more, the amount of additive re- EXAMPLE 1 quired to give a desired fire resistance will often be Compounds a p, and A to S the formulations of quite small e.g. 5 to 10 percent by weight because of which are shown in Tables 1 and 2 respectively were the co-operative effect-of the chrysotile asbestos fibres. made by extrusion compounding and granulating the One or fire retardant additives may be present in the extrudate. 150 mm X 13 mm X 3.0 mm test specimens compositions and it is preferred to use mixtures of were made from the granulate in each case by injection antimony trioxide with halogenated hydrocarbons. moulding and tested according to method 508A of BS Mixtures of antimony trioxide and decabromodiphenyl 2782. The results are shown in the Tables. are particularly preferred, the most preferred mixture The level of fire retardant additive in each composibeing one containing 3 parts by weight of decation is calculable by adding together the individual bromodiphenyl per part by weight of antimony trioxcontents of the additives. ide. I-Ialogenated hydrocarbons may be used alone or in In the Tables, the numerical superscripts designate admixture with fire retardant additives otherthan antithe following: mony trioxide. Also, useful fire retardant additives 1. 0.25 inch chopped glass fibre include boron and phosphorus compounds and any of 2. Decabromodiphenyl these may be used singly or in admixture with one or 3. DECI-ILORANE" is a trademark designating a more other fire retardant additive. material which is the double Diels-Adler reaction The compositions according to the invention may product of hexachlorocyclopentadiene and cycontain more than one thermoplastic polymer. Also the clooctadiene. compositions may contain conventional additives suchs 4. Rating according to BS 2782 method 508A: SE= as stabilisers for the polymer, fillers and pigments in self extinguishing, RTFP= resistant to flame propaddition to the fire retardant additive and asbestos agation. fibres. 5. Burns" Burning rate in mm/minute by above A method of testing the rate of burning of plastics is BS Test. described in method 508A of BS 2782 (1970). In it, a 6. Drips: B Bends; SE Severe bending. extinbar of the material 13 mm wide X 150 mm long X 1.5 guishes by burning drips falling away. 3.0 mm thick is used and two lines are scribed on one TABLE 1 Com- Propylene Glass Chrysotile Antho- Amosite DCB DE- Sb 0 Rating Burns Drips po- CHLOR- sition I-Iomopolymer Fibre phyllite ANE a 95 3.75 1.25 Burns 18 Yes b 90 7.50 2.50 Burns 24 Yes c 85 11.25 3.75 Burns 11 Yes d 15.0 5.0 RTFP 11 Yes* TABLE l-continued Com- Propylene Glass Chrysotile Antho- Amosite DCB DE- Sb 0 Rating Burns Drips po- CHLOR- sition Homopolymer Fibre phy11ite ANE e 71.3 23.7 3.75 1.25 Burns 25 Yes* f 67.5 22.5 7.50 2.50 RTFP Yes* g 63.8 21.2 11.25 3.75 RTFP 2 No h 71.3 23.7 3.75 1.25 RTFP 15 No i 67.5 22.5 7.50 2.50 SE No j 63.8 21.2 11.25 3.75 SE N0 k 71.3 23.7 3.75 1.25 Burns 30 Yes 1 67.5 22.5 7.50 2.50 Burns 28 Yes m 63.8 21.2 11.25 3.75 Burns Yes n 71.3 23.7 3.75 1.25 Burns 26 Yes 0 67.5 22.5 7.50 2.50 Burns 25 Yes p 63.8 21.2 11.25 3.75 RTFP Yes +-extinction time 120 seconds TABLE 2 Com- Propylene Glass Chrysotile An tho- Amosite DCB DE- Sb,0 Rating Burns Drips P CHLOR- sition Homopolymer Fibre phyllite ANE A 95 3.75 1.25 Burns 32 Yes B 90 7.50 2.50 RTFP Yes* C 85 11.25 3.75 RTFP 27 Yes* D 80 15.00 v 5.0 RTFP 26 Yes* E 55 3.75 1.25 Burns 24 Yes F 50 40 7.50 2.50 Burns 16 Yes G 40 11.25 3.75 RTFP 11 Yes H 55 40 3.75 1.25 Burns 10 No 1 40 7.50 2.50 RTFP 7 No J 45 40 11.25 3.75 SE N0 K 40 3.75 1.25 Burns 16 Yes L 50 40 7.50 2.50 Burns 14 Yes M 45 40 11.25 3.75 RTFP 9 SB N 55 40 3.75 1.25 Burns 15 SB 0 50 40 7.50 2.50 Burns 1 1 SB P 45 40 1 1.25 3.75 RTFP 8 B Q 55 40 3.75 1.25 RTFP 6 No R 50 40 7.50 2.50 SE No S 45 40 11.25 g 3.75 SE N0 TABLE 3 Composition High Density Glass Chrysotile DCB Sb 0 Rating Burns Drips Po1yethy1ene% Fibre a 95.0 0 0 3.75 1.25 Burns 20 Yes b 90.0 0 0 7.50 2.50 RTFP 10 Yes* c 85.0 0 0 l 1.25 3.75 SE Yes, drips extinguish d 82.0 0 0 13.50 4.50 SE Yes. drips extinguish e 71.3 23.7 0 3.75 1.25 Burns 15 Yes f 67.5 22.5 0 7.50 2.50 RTFP negligible No g 63.8 21.2 0 11.25 3.75 SE No h 71.3 0 23.7 3.75 1.25 SE No i 67.5 0 22.5 7.50 2.50 SE No j 63.8 0 21.2 11.25 3.75 SE No TABLE 4 Composition Po1ystyrene% Glass Chrysotile Y DCB Sb,0 Rating Burns Drips Fibre a 95.0 0 0 3.75 1.25 Burns 30 Yes b 90.0 0 0 7.50 2.50 Burns 25 Yes c 85.0 0 0 11.25 3.75 RTFP 20 Yes d 75.0 0 0 18.75 6.25 SE Yes, drips extinguish e 71.3 23.7 0 3.75 1.25 Burns 20 Yes f 67.5 22.5 0 I 7.50 2.50 RTFP 10 Yes* g 63.8 21.2 0 11.25 3.75 SE Yes, drips extinguish h 71.3 0 23.7 3.75 1.25 RTFP 10 No i 67.5 0 22.5 7.50 2.50 SE N0 j 63.8 0 21.2 11.25 3.75 SE No I TABLE 5 Com- Styrene/Acrylo- Glass Chryso- Antho- Amosite DCB Sb o Rating Burns Drips sition nitrile Fibre tile phyllite a 95.0 0 0 0 3.75 1.25 Burns 25 Yes 17 90.0 0 O 0 0 7.50 2.50 RTFP 15 Yes 6 85.0 0 O O 0 11.25 3.75 SE Yes, drips extinguish d 80.0 0 0 O 0 15.00 5.00 SE No e 71.3 23.7 0 0 0 3.75 1.25 RTFP 15 Yes, drips extinguish f 67.5 22.5 0 0 0 7.50 2.50 SE Yes, drips extinguish g 63.8 21.2 0 O 0 11.25 3.75 SE N0 11 71.3 0 23.7 0 0 3.75 1.25 SE No i 67.5 0 22.5 0 0 7.50 2.50 SE No 1 63.8 0 21.2 I 0 0 11.25 3.75 SE No k 71.3 0 O 23.7 0 3.75 1.25 RTFP 25 Yes 1 67.5 0 O 22.5 0 7.50 2.50 SE No In 63.8 0 0 21.2 0 11.25 3.75 SE No 11 71.3 0 0 0 23.7 3.75 1.25 RTFP 27 B o 67.5 0 0 0 22.5 7.50 2.5 SE No p 63.8 0 0 0 212 11.25 3.75 SE No TABLE 6 Com- Styrene/ Chrysotile Anthophyllite Amosite DCB DE- 519 0 Rating Burns Drips p o- CHLORANE sition Acrylonitrile A 75 2O 0 0 3.75 0 1.25 RTFP 16-30 No B 70 20 O O 7.50 0 2.50 SE No C 65 20 0 0 11.25 0 3.75 SE No D 70 20 0 0 10.0 0 0 SE NO E 70 20 O 0 0 10.0 0 RTFP 32 B F 70 0 0 20 0 0 RTFP 29 NO G 70 0 0 10 0 O RTFP B Compositions F and G compare unfavourably with D. showing that chrysotile asbestos is superior to anthophyllite and amosite in terms of the flame retardance imparted to the compositions.

TABLE 7 Composition Nylon 6 Glass Chrysotile DCB Sb O Rating Burns Drips Fibre a 95 O O 3.75 1.25 RTFP 15 Yes b 90 0 O 7.50 2.50 SE Yes* 0 85 0 0 11.25 3.75 SE No (1 80 0 0 15.00 5.00 SE N0 e 71.3 23.7 0 3.75 1.25 RTFP 20 Yes f 67.5 22.5 0 7.50 2.50 RTFP 10 Yes g 63.8 21.2 0 11.25 3.75 SE N0 h 71.3 0 23.7 3.75 1.25 RTFP 0 No i 67.5 0 22.5 7.50 2.50 SE No j 63.8 0 21.2 11.25 3.75 SE N0 Tables 1 and 2 illustrate the flame extinguishing effect of chrysotile asbestos fibre reinforcement and also the prevention of dripping of burning fragments. It also shows that reinforcement with glass fibre or other forms of asbestos has little flame suppressing effect.

EXAMPLE 2 The experiments described in Example 1 were repeated, but in this case high density polyethylene was used in place of polypropylene of Example 1. Table 3' shows the compositions tested and the results obtained.

EXAMPLE 3 The experiments described in Example 1 were re-v peated, but in this case polystyrene was used in place of polypropylene. Table 4 shows the compositions tested and the results obtained.

EXAMPLE 4 The experiments described in Example 1 were repeated, but in this case styrene-acrylonitrile copolymer was used in place of polypropylene. Tables 5 and 6 show the compositions tested and the results obtained.

EXAMPLE 5 The experiments described in Example 1 were repeated,b'ut in this case nylon 6 was used in place of polypropylene. Table 7 shows the compositions tested and the results obtained.

EXAMPLE 6 equivalent amount of glass fibre or of anthophyllite TABLE 8 or amosite asbestos. Pdyme' 9:355:5 gfig2g 21 When using chrysotile asbestos as reinforcement, "53nd! mixture); the amount of fire retardant agent necessary to give f extinguishing 5 achieve retardant properties equivalent to those of propemes a glass or anthophyllite or amosite reinforced mateyp py rial of equivalent fibre content, is at least half and 2 13:8 frequently much less than that necessary in the 40 glass, anthophyllite or amosite reinforced materiali Polyethylene $8 To understand the above conclusions, it is, ofcourse,

25 5:0 necessary to compare similar compositions, e.g. com- Polystyrene 8 2??) positions (h), (i) and (j) should be compared with 10 compositions (e), (f) and (g) respectively in each of 25 Tables 1, 3, 4, 5 and 7; compositions H, I, J and Q, R, Styrene, 8 21% 15 S, should be compared with the other respectively simiacrylonitrile 10 10.0 lar compositions of Table 2; and composition D should copolymer 2 5 be compared with F and G in Table 6. Further, it is seen Nylon 6 0 1010 by comparison of (h) with (k) and (h) in Table 5 that Palym"r g fig less fire retardant additive is required with chrysotile 40 asbestos than with other forms of asbestos, to achieve equivalent degrees of flame resistance. It is clear that anthophyllite and amosite asbestos act as inert fillers The Tables above show that chrysotile asbestos fibre Similar to glass fibre in respect of flame retardance is effective as a flame retardant additive, its value as a and do not exhibit the fire retardant P p ly Show y i f i fib f thermoplastic polymers is 11 equivalent amounts of chrysotile asbestos in otherwise trated in Table 9 identical compositions.

TABLE 9 Polymer Chrysotile Tensile Flexural Flexural Deasbestos strength strength modulus flection fibre (MN/m) (MN/m (GN/m) temperature content ("C Polypropylene 0 34 48 1.4 100 25 46 75 4.0 140 High density 0 41 1.2 82 polyethylene 25 45 4.5 l 18 Polystyrene 0 48 62 3.1 25 58 108 7.5 92 Styrene] 0 69 3.4 96 acrylonitrile 25 77 9.5 105 copolymer Nylon 6 0 76 No break 1.4 25 91 202 8.5 202 A further series of tests was effected, omitting the It Should b n ed hat the nature of the polymer fire-retardant additives, with the compositi ns nd I dictates the chrysotile asbestos fibre content therein, results shown in Table 10. 45 e.g. it is possible to disperse up to 45 percent or more by weight of chrysotile asbestos in polypropylene, but TABLE 10 the maximum workable content of chrysotile In the Polymer chrysotile Rating Bums P stiffer flowing polymers is about 30 percent although polypwpylene 0 R-rpp 33 Yes higher percentages can be achieved; it is preferred to :1 3 1 E 50 use not less than 25 percent by weight chrysotile asbes 28 No tos in polypropylene and nylon 6. 40 l8 No I claim: Polystyrene 0 U 43 1. A fire resistant thermo lastic com osition com- 5 46 S.B. P P 10 46 SB. prising i3 :1 3 g 55 a. from 40 to 90 percent by weight of a thermoplastic Nylon 6 0 15 E polymer selected from the group consisting of poly- 5 I: 20 Yes propylene, copolymers of propylene, polyethylene, 52 H polystyrene, styrene/acrylonitrile copolymers, 40 negligible No polyamides and mixtures thereof; and

50 b. a fire-retardant additive consisting essentially of i. from 5 to 40 percent by weight of chrysotile Analysis of the above Tables shows, inter alia the asbestos fibres; and following points. ii. from 2.5 to 20 percent by weight of an additive 1. When chrysolite asbestos is used as a reinforcing mixture of antimony trioxide and at least one agent in thermoplastics, the fire retardant proper- 65 halogenated hydrocarbon selected from the ties are improved in at least the rating or drips" group consisting of decabromodiphenyl and the tests, frequently in both, compared to the results double Diels-Alder condensation product of hexfor the tests where the reinforcing agent is an achlorocyclopentadiene and cyclooctadiene.

3. The fire-resistant composition of claim 1 wherein the additive mixture consists of at least 2.5 percent by weight, based on the total weight of the composition, of

a mixture of 3 parts by weight of a halogenated hydrocarbon and one part by weight of antimony trioxide. 

1. A FIRE RESISTANT THERMOPLASTIC COMPOSITION COMPRISING A. FROM 40 TO 90 PECENT BY WEIGHT OF A THERMOPLASTIC POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYPROPYLENE, COPOLYMERS OF PROPYLENE, POLYETHYLENE, POLYSTYRENE, STYRENE/ACRYLONITRILE COPOLYMERS, POLYAMIDES AND MIXTURES THEREOF; AND B. A FIRE-RETARDANT ADDITIVE CONSISTING ESSENTIALLY OF I. FROM 5 TO 40 PERCENT BY WEIGHT OF CHRYSOTILE ASBESTOS FIBRES; AND II. FROM 2.5 TO 20 PERCENT BY WEIGHT OF AN ADDITIVE MIXTURE OF ANTIMONY TRIOXIDE AND AT LEAST ONE HALOGENATED HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF DECABROMODIPHENYL AND THE DOUBLE DIELS-ALDER CONDENSATION PRODUCT OF HEXACHOROCYCLOPENTADIENE AND CYCLOOCTADIENE.
 2. The fire-resistant composition of claim 1 containing from 20 to 40 percent by weight of the chrysotile asbestos fibres and from 5 to 10 percent by weight of said additive mixture.
 3. The fire-resistant composition of claim 1 wherein the additive mixture consists of at least 2.5 percent by weight, based on the total weight of the composition, of a mixture of 3 parts by weight of a halogenated hydrocarbon and one part by weight of antimony trioxide. 